Conventional LED drive circuits typically are designed by adopting a switch-type power converter. Referring to FIG. 1, it employs a semiconductor power switch to switch low frequency AC or DC power signals to high frequency DC drive signals usable for LEDs. Such a high frequency conversion wastes a lot of energy on different converter elements and results in power loss. Moreover, the high frequency switch creates signal interference that requires more elements to suppress. As the prevailing trend of products mainly focuses on energy-saving and miniaturization, the structure of the switch-type power converter cannot fully meet the requirement of LED drive circuits.
Furthermore, the common voltage regulator circuit is typically used for constant current control that is widely adopted. The voltage regulator must share significant energy with the controlled constant current load to get desired control effect. As a result, it also consumes a lot of power that becomes a great concern for designing the power converter. When in use, in the voltage regulator circuits, the more power consumption of the elements, the higher the temperature. If the voltage regulator circuit is adopted in the LED drive circuits, the greater cooling mechanism is needed. This disobeys the requirements of energy-saving and miniaturization of the products. Thus there are still rooms for improvement.